FACIAL ANGLE. 



589 



in our considerations every class of animals in which the specialization 

 to be considered appears. For example, every animal belonging to the 

 vertebrate sub-kingdom of animals agrees with every other animal of 

 the same sub-kino-dom in the following distinctive characteristics — 

 characteristics, too, that we shall find involved in our considerations of 

 the subject of the facial angle : In all, the head and vertebral column 

 are composed of a number of definite segments, arranged along a longi- 



FlG. 1. 



tudinal axis ; each segment of this framework is normally composed of 

 a body and two diverging, ring-like formations ; the dorsal containing 

 the brain and spinal cord, the ventral, or abdominal, containing the or- 

 gans of nutrition, as the alimentary canal, circulating and eliminating 

 organs. Every vertebrate animal, then, is possessed of two tubes of 

 framework : the one, to protect the brain and spinal cord ; the other, 

 the organs of nutrition. These tubes are subject to very great varia- 

 tion, and are modified, as by a master's hand, to meet the necessities 

 that their various specializations of function may demand. The great 

 modification in the calibre of the dorsal tube in different classes of the 

 vertebrates, as well as the great variation in shape of the elements 

 which compose that arch, is apparent to every one. In the region of 

 the spine, the elements that compose the segments of the arch are 

 rounded, and at some distance apart, while in the cranial (skull) re- 

 gion they are flattened, spread out, so as to unite and form sutures, 

 thus making a solid brain-case, for the protection of the softer and 

 more massive nerve-matter. 



